The present invention is generally related to high pressure cells used for high pressure and spectroscopic studies and applications. More particularly, the present invention is directed to the use of moissanite in high pressure cells and high pressure presses.
High pressure cells generate static pressure by squeezing samples between a pair of anvils, which serve as spectroscopic windows. The generation of high pressure for research and development exploratory work has been influenced heavily by apparatus design and strength of materials. Professor Bridgman of Harvard found that he could reach pressures of about 100 Kbar by squeezing thinned samples between flat blocks. This work, starting about 50 years ago, led to the development of the famous Bridgman anvil. Bridgman recognized that if harder materials, such as sintered diamonds, were used for anvils, even higher pressures could be reached. Van Valkenburg and Weir at the National Bureau of Standards (NBS), Washington, D.C., unaware of Bridgman""s recommendation, made Bridgman anvils out of single crystal diamond in 1959. This started a revolution in high pressure work. Diamond anvil cells now are ubiquitous devices used throughout the world in high pressure research.
Twenty years later, Mao-Bell high pressure cells achieved pressures up to 500 Kbar utilizing anvils, each of which was a brilliant cut diamond of about one-third carat, the culet being polished to produce a flat of about 0.25 mm2 in area. The Mao-Bell cell was used in the first experimental efforts to break the 50 GPa and 100 GPa barriers. The first pressure calibrations of pressures up to 100, 170, 280, and 550 GPa, in non-hydrostatic conditions, and 80 GPa in quasi-hydrostatic conditions were also achieved using a Mao-Bell cell. In this regard, reference is made to the following publications which are expressly incorporated herein by reference: Bell P. M. et al., xe2x80x9cUltrahigh pressure: beyond 2 megabars and the ruby fluorescence scalexe2x80x9d, Science, 226, 542-544 (1984), and Xu, J. et al., xe2x80x9cHigh pressure ruby and diamond fluorescence: observations at 0.21 to 0.55 terapascalxe2x80x9d, Science, 233, 1404-1406, (1986).
Pressures approaching 360 GPa, equal to the pressure at the center of the earth, have also been reported by Ruoff et al, xe2x80x9cOptical Properties of Diamond at Pressures Comparable to the Earth""s Centerxe2x80x9d, Proceedings of the Second International Conference, New Diamond Science and Technology, Edited by Messier et al, September 23-27, Washington, D.C. Materials Research Society, Pittsburgh, Pa., the disclosure of which is expressly incorporated herein by reference.Experiments up to 300 GPa have become routine; experiments above 400 GPa are far less common, and generally not reproduced.
U.S. Pat. No. 5,295,402 issued to Bovenkirk teaches a method for achieving high pressure in a cell, wherein a sample is placed between a pair of diamond anvils and the anvils compressed. The invention of Bovenkirk involves forming the anvils from one or more of isotopically-pure 12C or 13C diamonds.
Diamond-anvil cells (xe2x80x9cDACxe2x80x9d) are well-known devices, which are used to study materials at high static pressures. In a typical DAC, two brilliant-cut diamonds, each with its culet point truncated to form a planar face, are compressed in opposition against one another. A deformable gasket, consisting of a flat piece of metal foil with a small hole in it, is placed between the opposing diamond faces, with the sample to be studied being contained in the hole in the foil and between the opposing diamond faces. Static pressures on the order of 600 kilobars can be readily obtained by mechanical compression of the diamonds. The primary advantage of the diamond-anvil cell is that the sample can be viewed through the two optically transparent diamonds, thus enabling spectroscopic and other optical studies to be conducted while the sample is compressed.
The construction and operation of conventional diamond anvil high pressure cells is now well known. In this regard, reference is made to the following publications which are expressly incorporated herein by reference: Field, The Properties of Diamond, Academic Press, New York City, N.Y. (1979); Manghnani, et al., High-Pressure Research and Mineral Physics, Terra Scientific Publishing Company, Tokyo, American Geophysical Union, Washington, D.C. (1987); Homan, xe2x80x9cHigher Pressure in Science and Technologyxe2x80x9d, Mat. Res. Soc. Symp. Proc., vol. 22, pp 2939, et seq., Elsevier Science Publishing Company (1984); Vodar, et al., High Pressure Science and Technology, Proceedings of the VIIth International AIRTAPT Conference, Le Creusot, France, July 30-Aug. 3, 1979, Pergamon Press, New York, N.Y.; Ruoff et al, xe2x80x9cThe Closing Diamond Anvil Optical Window in Multimegabar Researchxe2x80x9d, J. Appl. Phys., 69 (9), 6413-6415, May 1, 1991; Mao et al, xe2x80x9cOptical Transitions in Diamond at Ultrahigh Pressuresxe2x80x9d, Nature, Vol. 351, 721 et seq, Jun. 27, 1991; and Ruoffet al, xe2x80x9cSynthetic Diamonds Produce Pressure of 125 GPa (1.25 Mbar)xe2x80x9d, J. Mater. Res., 2 (5), 614-617, September/October 1987. Conventional opposed diamond anvil cells are fairly uniform in design with variations with respect to improved alignment and alignment adjustment being parameters that the operator can use in designing such cells.
Manghnani, et al., supra, state that improvements may be possible in diamond tip geometry, double beveling, and gasket design in order to achieve higher pressures. These authors further note that stronger diamonds would be desirable and speculate that some advances may be made through the use of synthetic diamonds. In this regard, reference is made to the following publications which are expressly incorporated herein by reference: Bell, P. M., Xu and H. K. Mao, in Shock Waves in Condensed Matter, Y. M. Gupta, Editor, Plenum Publishing Co., New York, p. 125 (1986); Hemley, R and Ashcroft, Physics Today, 51, 26, 1998; Hemley, R. et al., xe2x80x9cX-ray imaging of stress and strain of diamond, iron and tungsten at megabar pressuresxe2x80x9d, Science, 276, 1242-1245, 1997; Hirose, K. et al., Nature, 397, 53-56, 1999; Ito, E. et al., Geophys. Res. Lett., 25, 821-824, 1998; Mao, H. K. et al., alibration of the ruby pressure to 800 Kbar under quasi-hydrostatic conditionsxe2x80x9c, J. Geophysical Research, 91, 4673-4676, 1986; Pruzan, P. et al., Europhys. Lett., 13, 81, 1995; Xu, J. et al., Raman study on D2O up to 16.7 GPa in the cubic zirconia anvil cellxe2x80x9d, J. Ramon Spectroscopy, 27, 823-827, 1996a.
In the past two decades, DACs have pushed high-pressure research to the megabar pressure range, and have revealed new phenomena and new states of matter. The DAC however, also has severe intrinsic limitations that hinder the next level of progress. Perfect diamonds are only available in small sizes, thus restricting the sample chamber to a microscopic volume. For pressures above 30 GPa, the typical 0.3-carat diamond anvil can only hold nanoliter (10xe2x88x929 L) samples. Significantly larger diamonds are impractical as the cost rises as the square of the diamond weight, and perfect diamonds above 30 ct are simply unavailable at any cost. Tungsten carbide and sintered diamond anvils have been used in multianvil (Katsura, T. et al., xe2x80x9cDetermination of Fe-Mg partitioning between perovskite and magnesiowxc3xcstite, Geophys. Res. Lett., 23, 2005-2008 (1996)), and Paris-Edinburgh (Nelmes, R. J. et al., xe2x80x9cMulti-site disordered structure of ice VII to 20 GPaxe2x80x9d, Phys. Rev. Lett., 81, 2719-2722 (1998)) high-pressure apparati to contain microliter (10xe2x88x926 L) or larger samples, but these opaque polycrystalline anvils prohibit spectroscopic studies and are limited to pressures below 30 GPa for carbide and 50 GPa for sintered diamond.
The rarity and expense of diamonds for use in high pressure anvils continues to require that such devices utilize only very small anvils and restricts samples to microscopic size. There have been limited attempts to substitute diamonds with other spectroscopically complementary gem stones. It is now known that with limited pressures of 16.7 GPa for cubic zirconia and 25.8 GPa for sapphire, such substitutes fall well short of the desired pressure levels.
Diamond anvil cells play a major role in high-pressure research. However, it is difficult to study the high-pressure behavior of diamond itself, since the signal from the anvil diamonds seriously interfere with the sample diamond. Such is the case whenever the measured parameters are close to that of a diamond.
Thus a need exists to provide a low cost diamond substitute for use in high pressure anvils. To meet this need the inventors have provided a high pressure cell employing moissanite anvils (and/or moissanite gaskets), which results in improved analysis of larger samples and multiple samples, under extremely high pressure and at much lower cost. Further, the inventors have provided moissanite anvils for use in high pressure window material.
Accordingly, it is an object and purpose of the present invention to provide a high-pressure anvil cell employing moissanite as the anvil and spectroscopic window material.
Another object of the present invention is to provide a moissanite anvil for use in a high pressure anvil cell at variable temperatures.
Another object of the present invention is to provide a moissanite gasket for use in a high pressure anvil cell.
Another object of the present invention is to provide moissanite as a diamond substitute for industrial applications.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a novel high pressure anvil cell, which accommodates larger samples, and multiple samples, at lower cost than previously thought possible through the use of moissanite anvils and/or moissanite gaskets.